Introduce `BlockHeader` type class

[lehins]

We need a proper interface for the block header in order to make it safer and get rid of BHeaderView:

class EraBlockHeader h era | era -> h where
  blockHeaderSizeBHeaderL :: SimpleGetter (Block h era) BHeaderView
  blockIssuerBHeaderL :: LensSimpleGetter (Block h era) (KeyHash BlockIssuer)
  blockBodySizeBHeaderL :: Lens' (Block h era) BHeaderView
  ...

Then there would be separate type classes:

class EraBlockHeader h era => ShelleyEraBlockHeader h era where
  prevEpochNonceBHeaderL :: Lens' (Block h era) PrevEpochNonce

class EraBlockHeader h era => DijkstraEraBlockHeader h era where
   --- Peras related lenses

This would prevent ugliness like this: https://github.com/IntersectMBO/ouroboros-consensus/blob/1940605fbbfb50032ab78e2268b85065c703cd2a/ouroboros-consensus-cardano/src/shelley/Ouroboros/Consensus/Shelley/Protocol/Praos.hs#L196-L202
Where we have a bottom in bhviewPrevEpochNonce
And ugliness like this: #5467 (comment)